1. Field of the Invention
This invention relates to a storage rack for spent nuclear fuel assemblies.
2. Description of the Prior Art
Storage racks for nuclear fuel assemblies are described in U.S. Pat. Nos. 4,010,375, 4,177,385, 3,859,533, 4,039,842, 4,029,968, 4,004,154. The objective of each of these prior art storage racks is to provide a safe facility for confinement of spent nuclear fuel rods in water pools for extended periods until the residual radioactive emissions are reduced to a level at which the fuel assemblies can be safely removed. To prevent unwanted concentrations of neutrons, it is a common practice to position neutron poison materials within the storage racks to isolate neutrons into restricted regions of the storage rack, thereby permitting greater numbers of fuel rod assemblies to be confined safely within an established aqueous storage pool.
The storage racks typically include square or rectangular cross-section tubes which are positioned vertically in the aqueous pool, parallel to each other. The individual tubes are secured into the storage rack. Typical neutron poison materials are boron carbide, aluminum-boron, cadmium, gadolinium. A particularly useful neutron poison material, Boroflex, is a silicone rubber pad having boron carbide particles homogeneously dispersed therein.
Typically the supporting racks will contain up to about 300 individual spent nuclear fuel rod assemblies. Typical fuel rod assemblies are from about 8 to 15 feet, long and about 1 to 9 inches square, each containing from 49 to 39 fuel rods. A typical aqueous storage pool has concrete walls and may be 40 feet deep.
There is a continuing need to increase the number of spent fuel rod assemblies which can be accumulated in one location, i.e. to increase the number of spent fuel rods in the volume of an available aqueous storage pool. Similarly there is a need to produce storage racks which reliably resist mechanical vibrations which may be applied to the storage rack from whatever source, but particularly to resist seismic vibrations due to local earthquake conditions.